It is known that various disorders are caused by various mineral deficiencies in plants such as fruit trees, fruit vegetables, leaf vegetables, and root vegetables. Examples of disorders caused by a calcium deficiency include bitter pit in apples, peel puffing in citrus fruits, blossom-end rot in tomatoes or bell peppers, fermented or deformed fruits in melons or water melons, tip burn in strawberries, blackheart in lettuces or celery cabbages, and burned tip in flowering plants. On the other hand, magnesium is an essential element required in large quantities by plants and is also a central element of a chlorophyll composition. Magnesium deficiency reduces photosynthesis, and therefore reduces the growth of plants. Furthermore, when a plant is cultivated on alkali soil, iron deficiency is likely to develop and leads to various disorders.
Calcium is an essential nutrient for plants because it is, for example, a component of cell walls of plants. In recent years, however, acidification of soil is likely to occur due to an effect of acid rain and the like, and this situation would be extremely likely to cause a symptom of calcium deficiency in plants. In order to solve this problem, a method for fertilizing soil with calcium is provided. However, calcium is a nutrient whose rate of transport within a plant is very slow, and therefore it is difficult to obtain an effect of calcium fertilization immediately after fertilizing soil when a symptom of calcium deficiency develops in a specific part of the plant. In order to solve this problem, a method of spraying a calcium preparation and the like onto a leaf surface and the like has been taken so as to allow calcium and the like to be absorbed directly into a nutrient-deficient part of the plant.
Water-soluble calcium, such as calcium chloride and calcium nitrate, is conventionally used as a leaf application. However, these calcium preparations have a problem that their counter ions such as chlorine ions and nitrate ions will cause phytotoxicity. In order to avoid this problem of phytotoxicity, it has been proposed to use a water-soluble calcium preparation containing, for example, calcium formate as an active ingredient (for example, Patent Document 1). This method can solve the problem of phytotoxicity due to the counter ions, however, absorption of calcium is far from sufficiency. That is, it is not necessarily effective for resolution of bitter pit in apples, for example.
Furthermore, it has been proposed to use a water-soluble solid preparation containing calcium carbonate and one or more organic acids selected from the group consisting of citric acid, malic acid, tartaric acid, gluconic acid, succinic acid, malonic acid, glutaric acid, maleic acid, fumaric acid and glutaconic acid (for example, Patent Document 2). In this method, calcium carbonate solubilized in water with the help of various organic acids is used as a source of calcium in order to solve the problem of phytotoxicity due to the counter ions such as calcium chloride. In this method, however, calcium carbonate is used in a form of an aqueous solution having an acidic pH of, for example, pH 1.5. Therefore, there is a problem that fruit or leaf burn caused by acid is likely to occur and acidification of soil is also likely to occur. This method, therefore, is not necessarily preferred.
It has been proposed to use a preparation formulated with 5 to 40 wt % of water-soluble calcium salts and 1 to 10% of a spreading organic polymer, based on calcium carbonate having a particle diameter of not less than 0.6 μm and not more than 2.8 μm, as a quality improver for fruits (for example, Patent Document 3). In the case of this method, calcium carbonate and water-soluble calcium salts are suspended in water to be used as the preparation. However, a specific gravity of calcium carbonate is as large as 2.7, and the resulting preparation is not necessarily in a good dispersion state. Therefore, there is a problem that suspended solids in water are likely to precipitate at a bottom of a container. In the case of using this preparation, an effect of preventing peel puffing is likely to be non-uniform and is far from sufficiency due to the above problem. Further, using this preparation, there is also a problem that a surface of a fruit is soiled whitish due to mainly coarse particles and secondary aggregates of calcium carbonate and the like, which are generated by spraying the preparation and evaporating to dryness. Therefore, there is a problem that much work is needed to wipe off the whitish dirt.
It has been proposed to use a calcium fertilizer for leaf application containing a highly soluble calcium salt and a poorly soluble calcium salt in a ratio of 10 to 50%:90 to 50% (for example, Patent Document 4). According to this method, phytotoxicity can be reduced by using a fertilizer containing a highly soluble calcium salt and a poorly soluble calcium salt in a predetermined ratio. However, a counter ion responsible for the phytotoxicity is present in a certain quantity in the fertilizer and therefore, a problem of the phytotoxicity is far from being completely solved. Further, this method is far from being fully effective, as in the method described in Patent Document 1, to overcome a physiological disorder such as bitter pit, since this is only a method of spraying a calcium preparation having a low possibility of causing the phytotoxicity. Although this method provides a certain level of effect for preventing peel puffing, it is also far from being fully effective as in the method described in Patent Document 1. There is also a drawback that the calcium preparation cannot be used in combination with a phosphate fertilizer, since they would react with each other.
There has been proposed a method for preventing apple flesh browning during cold storage. This method includes applying, to a surface of an apple, a suspension which contains calcium phosphate having a particle size of not more than 10 μm and a molar ratio of Ca/P in the range of 0.8 to 1.5 (for example, Patent Document 5). In this method, the particle size is reduced using a grinding machine. However, there is a limitation in the reduction of the particle size, and the remaining coarse particles without being ground cannot contribute to producing the desired effect. Therefore, it is difficult to obtain a sufficient effect in this method.
In the case of using a magnesium preparation, on the other hand, there is the same problem as with a calcium preparation. That is, the use of a water-soluble magnesium preparation such as magnesium chloride, magnesium nitrate and magnesium sulfate is not preferable since counter ions such as chlorine ions, nitrate ions and sulfate ions causes phytotoxicity.
In order to solve this problem, a magnesium fertilizer containing magnesium acetate has been proposed (for example, Patent Document 6). According to this method, the phytotoxicity can be reduced. However, the spraying effect is far from sufficiency, as with the calcium preparation, by merely spraying an aqueous solution of the magnesium preparation. In addition, there is a drawback that the effect of a water-soluble magnesium preparation is likely to be affected by the weather, since the preparation would easily run off by rain.
As an iron preparation, on the other hand, organic chelated iron has been used for leaf application or soil application. However, organic chelated iron is expensive and the reality is that the adoption rate is very low.
Patent Document 1: Japanese Examined Patent Publication No. S62-28117
Patent Document 2: Japanese Unexamined Patent Publication No. 2004-238248
Patent Document 3: Japanese Examined Patent Publication No. S59-19923
Patent Document 4: Japanese Patent No. 2563067
Patent Document 5: Japanese Examined Patent Publication No. H2-33349
Patent Document 6: Japanese Unexamined Patent Publication No. H6-172069